Speed Converter

How do you convert speed units?

To convert speed units, multiply by the starting unit's value in meters per second, then divide by the target unit's value in m/s. A speed is a distance divided by a time, so every speed unit can be written as a number of meters per second. The factors are exact because the mile, foot and nautical mile are all defined in meters, and the hour is exactly 3,600 seconds.

A worked example

To convert 60 mph to km/h: 60 × 0.44704 = 26.8224 m/s. One km/h is 1,000 m ÷ 3,600 s, or 0.2777… m/s, so 26.8224 ÷ 0.2777… = 96.56064 km/h. The single shortcut factor is 1.609344, the number of kilometers in a mile, which you can apply directly in the mph to km/h converter. Going the other way, multiply km/h by about 0.621371 to get mph, as the km/h to mph converter does.

Why meters per second and km/h differ by 3.6

One kilometer per hour is 1,000 meters covered in 3,600 seconds. Dividing gives 1 km/h = 1/3.6 m/s, so you multiply m/s by 3.6 to get km/h and divide km/h by 3.6 to get m/s. A 100 km/h highway speed is about 27.78 m/s, which is why physics problems and wind reports in m/s look smaller than road signs. The m/s to km/h converter handles this in one step.

Mach is not a fixed speed

Mach number is the ratio of an object's speed to the local speed of sound, and the speed of sound in air rises and falls with temperature. This converter uses 340.29 m/s, the value for dry air at sea level at 15 °C in the International Standard Atmosphere, which gives Mach 1 ≈ 1,225.04 km/h ≈ 761.21 mph. At 11,000 m, where the standard atmosphere is −56.5 °C, sound travels at only about 295 m/s, so Mach 1 there is roughly 660 mph. Treat any Mach to mph result as a sea-level figure unless you adjust for altitude.

What is the SI unit of speed, and how do the units relate?

The SI unit of speed is the meter per second (m/s), a derived unit made from the meter and the second. The BIPM SI Brochure defines both base units through fixed constants of nature, so a meter per second means the same thing in every laboratory. Kilometers per hour are not SI, because the hour is not an SI unit, but the SI Brochure accepts the hour for use with the SI, which is why km/h appears on road signs worldwide.

Several of these relationships are exact fractions. One mile per hour is exactly 22/15 feet per second, which is why 60 mph is exactly 88 ft/s, and one knot is exactly 1,852 meters per hour. One m/s is exactly 3.6 km/h, while the mph and knot factors run to many decimals because they mix customary and metric lengths. NIST SP 811 gives 1 mph as exactly 0.44704 m/s, and the knot works out to 1,852/3,600 m/s, about 0.514444 m/s. For sailing and flying speeds, the knots to mph converter applies the factor for you.

Where is each speed unit used?

Kilometers per hour rule the roads in most of the world, miles per hour in the US and UK, knots at sea and in the air, and meters per second in science. Which unit you meet depends on the vehicle as much as the country.

• Miles per hour (mph): road speed limits and car speedometers in the United States and the United Kingdom, plus a handful of other countries and territories. Baseball pitch speeds and wind speeds in US weather reports also use mph.
• Kilometers per hour (km/h): road signs, vehicle speedometers and train speeds in nearly every other country, including Canada, Australia, India and all of continental Europe.
• Knots (kn): ships, aircraft airspeed and marine weather worldwide. Because one knot is one nautical mile per hour, and a nautical mile is about one minute of latitude, knots fit neatly with charts. See the knots to mph converter for boating and flight speeds.
• Meters per second (m/s): physics, engineering and science, and wind speed in many national weather services and wind-turbine specifications.
• Feet per second (ft/s): ballistics, fluid flow in US engineering, and elevator or conveyor speeds.
• Mach: aircraft and rocket speeds near or above the speed of sound, where the ratio to local sound speed matters more than the raw number.

What is the difference between speed, velocity and pace?

Speed tells you how fast something moves, velocity adds a direction, such as 20 m/s due north, and pace turns the ratio around into time per distance. The units are the same, so this converter works for both. Runners and cyclists often think in pace instead, which is time per distance rather than distance per time. A 5:00 per kilometer pace is 12 km/h, and an 8:00 per mile pace is 7.5 mph. To turn a pace into a speed, divide 60 by the minutes per unit of distance.

Everyday speeds for reference: a brisk walk is about 5 km/h (roughly 3.1 mph), the fastest recorded 100 m sprints peak a little above 12 m/s (close to 28 mph), a cruising airliner flies near Mach 0.8, and a container ship typically sails at around 15 to 25 knots. If you also need to convert the distances behind these speeds, the length converter covers miles, kilometers and nautical miles.

How do you calculate speed from distance and time?

Speed equals distance divided by time, so time equals distance divided by speed, and distance equals speed times time. The only rule is to keep the units consistent: kilometers with hours give km/h, miles with hours give mph, and meters with seconds give m/s.

• Speed: a marathon of 42.195 km finished in 4 hours is an average of 10.55 km/h, or 6.55 mph.
• Time: 300 km at 100 km/h takes 3 hours; 250 miles at 65 mph takes 3.85 hours, which is 3 hours 51 minutes.
• Distance: 45 minutes at 80 km/h covers 0.75 × 80 = 60 km.

When a trip is given in minutes, turn the minutes into decimal hours first; the minutes to hours converter does that step, and the time converter covers seconds, days and weeks.

The average-speed trap

Averaging two speeds does not give the average speed. Drive a fixed distance out at 60 mph and back at 40 mph, and the round-trip average is 48 mph, not 50 mph, because you spend longer at the slower speed. Always divide total distance by total time. The same logic applies to fuel use over a trip, which the fuel economy converter handles in mpg and L/100 km.